1. Field of the Invention
The present invention relates to a power transmission apparatus for a vehicle.
2. Description of Related Art
A mechanism capable of reducing noise in a spline-fitting section that connects a rotary shaft of an electric motor and a drive shaft (rotary shaft) has been known (see Japanese Patent Application Publication No. 2011-214646 (JP 2011-214646 A), for example).
The mechanism that is disclosed in JP 2011-214646 A above includes a drive source (an engine), a generator, and an electric motor as primary components. The rotary shaft of the electric motor is spline-fitted to the drive shaft that is coaxially arranged. The drive shaft is indirectly connected to the drive source. The drive shaft is configured such that output torque of the drive source is transmitted thereto.
An inner spline is formed on an inner peripheral side at an end of the rotary shaft of the electric motor. An outer spline is formed on an outer peripheral side at an end of the drive shaft. The inner spline of the rotary shaft in the electric motor and the outer spline of the drive shaft are connected (spline-fitted) to each other.
An O-ring is provided for an entire circumference in a portion in which the end of the rotary shaft in the electric motor and the end of the drive shaft overlap each other and that is other than the spline-fitting section.
In a case where the electric motor does not output torque (or outputs minute torque), a fluctuation in torque (a fluctuation in rotation) that is output by the drive source causes abutment of a gear pair that is arranged upstream of the spline-fitting section in a torque transmission path, and further causes generation of the noise when the inner spline of the rotary shaft in the electric motor abuts against the outer spline of the drive shaft. At this time, the O-ring, which is provided between the rotary shaft in the electric motor and the drive shaft, alleviates shock, and the noise is thereby reduced (suppressed).